PROJECT SUMMARY Dopamine is a, neurotransmitter that has been implicated in multiple neurological and psychiatric disorders in the. CNS. The various actions of DA on target neurons are mediated via prototypical 7-transmembrane G protein-Coupled receptors (GPCR) that couple to various effector systems, Therapeutic agents, including all clinically effective antipsychotics, interact with DA D2 receptors (D2R) and elicit both beneficial and unwanted side effects. In previous work, we have demonstrated that striatal D2Rs on medium spiny nervous (MSN) mediate- some of their actions through both G protein-dependent and independent mechanisms. These G protein-independent action occur through formation of B-arrestin2-dependent signaling complexes with components of the AKt/GSKS signaling pathway. Work during our previous U-19 NCDD grant period has identified novel small molecules based on, the scaffold of the anti-phychotic drug aripipraziole that can act as FUNGTIONALLY SELECTIVE ligands at theDb2R. These D2R are ligands are agonists at the G protein-mediated inhibition of cAMP production as well as antagonists at D2R/B-arrestin2 interactions or vice versa. Moreover, using pharmacologicai or genetic mouse rnodels of hyperdopaminergic function, compounds that are selective D2R/B arrestin2 interactions show potent antipsychotic activity profiles without associated cataleptic side effect. By comparison, these .these compounds elicit significant side effects in B-arrestin2 knockout mice where b2R/p-arrestih2 interactions are absent. These results suggest; that D2R;/B-arrestin2 signaling may protect against these unwanted effects. In Project 2, we will use cell and brain-region selective inactivation or rescue of components of the,D2R signaling pathways to validate our initial results and to determine the cellular and molecular events responsible for the antipsychotic profile(s) of the newly discovered functionally-selective D2R ligands. Aim 1: We will validate new mouse models of D2R/antipsychotic action through the use of mice in which B-arrestin2 and GSK3B have been selectively inactivated in D2R expressing in various neuronal populations; Aim 2: We will profile the new ligands in mice in which the endogenous D2R has been virally replaced by wild type B2R or a mutated D2R capable of selectively coupling to G protein or p-arrestin2 signaling. Aim 3; We will determine the cellular-and molecular profiles of the novel antipsychotic drugs by examining the biochemical, physiological and cellular events that correlate with the beneficial /side-effect actions of these agents in bur various animal model's. We anticipate that these efforts will lead to the proof-of-concept that targeting D2R/B-arrestin2 signaling will provide novel ligands for the development of more selective and effective therapeutic agents for clinical studies.